- Stereodependent and solvent-specific formation of unusual β-structure through side chain-backbone H-bonding in C4(S)-(NH2/OH/NHCHO)-L-prolyl polypeptides
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It is shown that C4(S)-NH2/OH/NHCHO-prolyl polypeptides exhibit PPII conformation in aqueous medium, but in a relatively hydrophobic solvent trifluoroethanol (TFE) transform into an unusual β-structure. The stereospecific directing effect of H-bonding in defining the specific structure is demonstrated by the absence of β-structure in the corresponding C4(S)-guanidinyl/(NH/O)-acetyl derivatives and retention of β-structure in C4(S)-(NHCHO)-prolyl polypeptides in TFE. The distinct conformations are identified by the characteristic CD patterns and supported by Raman spectroscopic data. The solvent dependent conformational effects are interpreted in terms of intraresidue H-bonding that promotes PPII conformation in water, switching over to interchain H-bonding in TFE. The present observations add a new design principle to the growing repertoire of strategies for engineering peptide secondary structural motifs for innovative nanoassemblies and new biomaterials.
- Bansode, Nitin D.,Madhanagopal,Sonar, Mahesh V.,Ganesh, Krishna N.
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- Spiegelmeric 4R/S-hydroxy/amino-L/D-prolyl collagen peptides: conformation and morphology of self-assembled structures
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The primary structure of collagen, the major protein in connective tissue of mammals, comprises of repeating triads [(LPro-LHyp-Gly)n, P1, LHyp being 4R-hydroxy-lProline)] in a single strand that adopts left-handed polyproline II type helix. Three such single stranded helices wind around each another and held together by interchain H-bonds to form right-handed triple helix. This manuscript reports on collagen derived from its mirror image triad [(DPro-DHyp-Gly)n, P2, DHyp being 4S-hydroxy-DProline) and its 4-amino analogue (DPro-DAmp-Gly)n P4, DAmp being 4S-amino-DProline that form corresponding spiegelmeric triplexes. The amino L-collagen peptide (LPro-LAmp-Gly)n P3 and its D-analogue P4 show higher thermal stabilities compared to 4-hydroxy-lProline collagen peptides P1 and P2. The enantiomeric peptide pairs show mirror image CD profiles and identical thermal stability, with ionizable 4-amino group in P3 and P4 imparting pH dependent triplex stability. Upon cold mixing of the L- and D-collagen peptides, different morphological nanostructures arise from inter triplex peptide association. When the peptides are hot mixed (annealed), the inter peptide association occurs via interaction of single stranded peptide chains of opposite handedness leading to networked gel formation in P1 and P2, while the charged peptides P3 and P4 show more ordered nanofibers, different from the enantiomerically pure peptides. The nanocomposites of such chiral hybrid peptides may have not only interesting physicomorphology, but also biological properties that need exploration.
- Ganesh, Krishna N,More, Shahaji H
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- Conformational changes associated with post-translational modifications of pro143 in Skp1 of dictyostelium -a dipeptide model system
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Prolyl hydroxylation and subsequent glycosylation of the E3SCF ubiquitin ligase subunit Skp1 affects its conformation and its interaction with F-box proteins and, ultimately, O2-sensing in the organism. Taking a reductionist approach to understand the molecular basis for these effects, a series of end-capped Thr-Pro dipeptides was synthesized, tracking the sequential post-translational modifications that occur in the protein. The conformation of the pyrrolidine ring in each compound was gauged via coupling constants (3JHα,Hβ) and the electronegativity of the Cγ-substituents by chemical shifts (13C). The equilibrium between the cis-trans conformations about the central prolyl peptide bond was investigated by integration of signals corresponding to the two species in the 1H NMR spectra over a range of temperatures. These studies revealed an increasing preference for the trans-conformation in the order Pro a reduced rate for the trans-to-cis conversion and a significant increase in the cis-to-trans conversion upon hydroxylation of the proline residue in the dipeptide. NOE experiments suggest that the Thr side chain pushes the sugar away from the pyrrolidine ring. These effects, which depended on the presence of the N-terminal Thr residue, offer a mechanism to explain altered properties of the corresponding full-length proteins.
- Karunaratne, Chamini V.,Weldeghiorghis, Thomas K.,West, Christopher M.,Taylor, Carol M.
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supporting information
p. 15170 - 15175
(2015/02/19)
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- The aberrance of the 4 S diastereomer of 4-hydroxyproline
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Prolyl 4-hydroxylases install a hydroxyl group in the 4R configuration on the γ-carbon atom of certain (2S)-proline (Pro) residues in tropocollagen, elastin, and other proteins to form (2S,4R)-4-hydroxyproline (Hyp). The gauche effect arising from this prevalent post-translational modification enforces a Cγ-exo ring pucker and stabilizes the collagen triple helix. The Hyp diastereomer (2S,4S)-4-hydroxyproline (hyp) has not been observed in a protein, despite the ability of electronegative 4S substituents to enforce the more common Cγ-endo ring pucker of Pro. Here, we use density functional theory, spectroscopy, crystallography, and calorimetry to explore the consequences of hyp incorporation on protein stability using a collagen model system. We find that the 4S-hydroxylation of Pro to form hyp does indeed enforce a Cγ-endo ring pucker but a transannular hydrogen bond between the hydroxyl moiety and the carbonyl of hyp distorts the main-chain torsion angles that typically accompany a Cγ-endo ring pucker. This same transannular hydrogen bond enhances an nφ* interaction that stabilizes the trans conformation of the peptide bond preceding hyp, endowing hyp with the unusual combination of a Cγ-endo ring pucker and high trans/cis ratio. O-Methylation of hyp to form (2S,4S)-4-methoxyproline (mop) eliminates the transannular hydrogen bond and restores a prototypical Cγ-endo pucker. mop residues endow the collagen triple helix with much more conformational stability than do hyp residues. These findings highlight the critical importance of the configuration of the hydroxyl group installed on Cγ of proline residues.
- Shoulders, Matthew D.,Kotch, Frank W.,Choudhary, Amit,Guzei, Ilia A.,Raines, Ronald T.
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experimental part
p. 10857 - 10865
(2010/09/17)
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